The curing of monomeric materials to produce polymeric thermoset resins is well known in the art. In general, the polymerizable monomers have one and customarily more than one reactive group which serves as an active site for a curing or crosslinking polymerization to produce the cured or thermoset resins. Crosslinking of many if not most of the polymerizable monomers requires the use of a second polymerizable monomer, e.g., a stoichiometric curing agent, to cause the curing to occur at an acceptable rate. The stoichiometric curing agent is employed in substantial quantities and will greatly influence the properties of the cured product.
Other polymerizable monomers will cure without the presence of a curing agent and are termed "self-curing." These monomers are also frequently cured with other polymerizable monomers in order to obtain more desirable properties. One class of self-curing monomers contain arylcyclobutene moieties, most frequently benzocyclobutene moieties. It appears likely that such materials undergo, on application of heat, ring opening of the four-membered ring to form very reactive intermediates which crosslink through reaction with adjacent molecules. The arylcyclobutene monomers also undergo reaction with a wide variety of unsaturated species such as maleic anhydride, maleimides, organic cyanates and allyl ethers. The products are thermoset resins having good properties of shelf-life and high use temperatures.
One class of such benzocyclobutene materials is disclosed by a series of U.S. patents to Kirchhoff of which U.S. Pat. No. 4,540,763 is illustrative. The disclosed compounds are characterized by direct linkages from the six-membered ring of the benzocyclobutene through a functional group to the remainder of the molecule. Reaction of such benzocyclobutene derivatives with bismaleimides is shown by Hahn et al, U.S. Pat. No. 4,730,030. A somewhat different class of benzocyclobutene derivatives is shown by copending U.S. patent application Ser. No. 349,546, filed May 9, 1989, wherein the six-membered ring is connected through an alkylene group to the remainder of the molecule. Specifically disclosed and claimed are benzocyclobutenealkyl ethers of bisphenols.
The class of organic dicyanates is a class of reactive polymerizable monomers which typically crosslink to form trimerized cyanurate resins which are highly crosslinked. The thermally cured products have high glass transition temperatures but also exhibit brittleness which renders the cured products unsuitable for some applications. For structural applications the cyanate resins are toughened by blending with up to 50% by weight of thermoplastic engineering thermoplastics as tougheners. However, conventional thermoset processing becomes difficult if not impossible at concentrations of thermoplastic greater than about 20% by weight because of viscosity problems. It would be of advantage to provide an alternate method of toughening cyanate resins.